1. Field of the Invention
The present invention relates to titanium trichloride catalytic complexes useful as a catalyst component for the stereoregular polymerization of alpha-olefins and more particularly pertains to a novel process for preparing a titanium trichloride catalyst complex having excellent alpha-olefin polymerization properties, e.g., stereospecificity, catalytic efficiency and narrow particle size distribution, in high yields.
2. Discussion of the Prior Art
As a method of producing crystalline polyolefin, it has been widely known to use a polymerization catalyst system comprising, in combination, a catalyst component consisting of a low valence transition metal halide and an organo-metal halide compound. More particularly, on a commercial scale, a titanium trichloride composition has conventionally been used as the low valence metal halide in combination with an aluminum alkyl compound as co-catalyst or activator.
There are many techniques described in the literature for preparing a titanium trichloride composition useful as catalyst in alpha-olefin polymerization. Generally speaking, several of such techniques include reducing titanium tetrachloride with hydrogen or aluminum powder at high temperature, followed by crushing the resulting reduced product for activation. Such catalyst components are widely used commercially, but leave much to be desired. More particularly, the polymerization speed and stereoregularity of such titanium trichloride catalysts require the utilization of a large amount of the expensive catalyst in alpha-olefin polymerization which a great cost is simultaneously required for treatment of non-crystalline polymers produced as byproduct. Moreover, the grinding step required in activating such titanium trichloride compositions results in wide particle size distribution so that polymer obtained by using such catalyst components also has wide particle size distribution, resulting in trouble in handling such polymers.
Many efforts have been made to overcome the aforementioned disadvantages. As a method of modifying the titanium trichloride composition, it has been proposed to add metal halides, alkyl aluminum compounds, halogenated hydrocarbons, ethers, esters, ketones, etc. More specifically, several references have described reduction of titanium tetrachloride with aluminum metal in the presence of certain halogenated hydrocarbons or treating the reduced product therewith. See, for example, U.S. Pat. No. 3,365,434.
It has also been proposed to add certain halogenated hydrocarbons to aluminum metal or hydrogen reduced titanium trichloride prior to or during the grinding-activation step. See U.S. Pat. No. 3,701,763; U.S. Pat. No. 3,560,146; British Pat. No. 1,414,312 and Japanese Pat. J7600097, both to Mitsubishi Petrochemical Company Ltd.; U.S. Pat. No. 3,875,126; Japanese application 64/24272, published 10-29-64, to Mitsui Chemical. Further, other references have described extracting resulting ground or pulverized aluminum metal reduced titanium trichloride compounds with certain halogenated hydrocarbons. See U.S. Pat. No. 3,701,763; 3,850,899; and British Pat. Nos. 1,336,770; 1,359,328; and 1,351,822, to name a few.
These methods, as well as others described in the literature employing other modifiers as mentioned hereinbefore, however, have not overcome the disadvantages associated with such titanium trichloride catalysts. Such modifications have not sufficiently improved particle size distribution, stereospecificity and catalytic activity of such catalysts.
Other techniques known in the art for preparing titanium trichloride catalyst components, generally speaking, include reducing titanium tetrachloride with an organo-metal compound, particularly an organoaluminum compound, at low temperature. Such techniques have the advantage in producing a catalytic component with a relatively even particle size; however, the resulting titanium trichloride composition obtained is normally a brown beta-crystalline type titanium trichloride with alpha-olefin polymerization properties which are very inferior. However, as known, such brown beta-type titanium trichloride compositions can be activated by crystal conversion to a more active violet, or purple, titanium trichloride normally having predominant alpha, gamma or delta crystalline structures.
More particularly, it is known that the brown beta-type titanium trichloride can be converted to more active, i.e., more stereospecific, higher catalytic activity, violet titanium trichloride by heating at not greater than about 200.degree. C., usually about 150.degree.-160.degree. C. See, for example, U.S. Pat. Nos. 2,971,925 to Winkler et al, 3,261,821 to Vanderberg, 3,562,239 to De Jong et al and 3,979,372, to name a few. However, as known, the polymerization properties of polymerization speed and stereoregularity of such TiCl.sub.3 compounds when used as a polymerization catalyst are not superior to the aforementioned aluminum-reduced pulverized titanium trichloride compositions.
Another technique for activating beta-type titanium trichloride compounds prepared by organo-metal reduction of TiCl.sub.4 which has developed considerable interest in the industry has been described in British Pat. Nos. 1,391,067 and 1,391,068 to Solvay et Cie. Thus, in these patents, there is described a method of preparing a catalyst component capable of giving relatively high polymerization speed, high stereoregularity and excellent particle size distribution by reducing titanium tetrachloride with an aluminum alkyl halide at low temperature to form a beta-type titanium trichloride composition and then treating it with a complexing agent and titanium tetrachloride to convert into a violet delta-type catalyst solid. However, this method has the disadvantage that, in order to get high polymerization activity, it is necessary in the activation step to use titanium tetrachloride in high concentrations of 15% by volume or more, preferably 30-40% by volume, as described in the patents. Moreover, it has been found that when using a complexing agent other than diisoamyl ether, the activated titanium trichloride composition is not substantially improved. Furthermore, when certain ethers are substituted, e.g., n-butyl ether, severe fracturing of the catalyst solids occurs with the required high concentrations of titanium tetrachloride. As known, diisoamyl ether and titianium tetrachloride reagents are expensive, thus the production costs of a satisfactory catalyst component in accordance with this described method on a commercial scale is high. Moreover, the necessary employment of titanium tetrachloride in high concentrations in the aftertreatment step presents safety hazards.
Yet another technique for activating beta-type titanium trichloride compounds, obtained by organo-metal reduction of TiCl.sub.4 at low temperature, has been proposed which includes treating the beta-type titanium trichlorides with certain halogenated hydrocarbons. More particularly, in Japanese Pat. Nos. J-50108-383 and J-50108-384 to Mitsubishi Petrochemical Company Ltd. (1975), a process is described in which TiCl.sub.4 is reduced at low temperature with an aluminum alkyl halide and the resulting brown precipitate is aftertreated with isoamyl ether or alcohol and carbon tetrachloride to give a red-purple solid which allegedly has excellent alpha-olefin polymerization properties.
Similarly, Japanese Patent JA-7206409 (1972) to Mitsui Petrochemical Co. describes a method whereby titanium tetrachloride is reduced with an organoaluminum halide in the presence of a halomethane, e.g., CCl.sub.4, HCCl.sub.3, etc., or the halomethane added to the reduction slurry, followed by heating.
Additionally, Japanese Pat. No. J 51030593 to Mitsubishi Chemical Ind. K.K. discloses treating an organoaluminum reduced TiCl.sub.4 solid with a complex-forming agent, e.g., an ether, and carbon tetrachloride or titanium tetrachloride.
In recently published Belgian Pat. No. 842,591 to Shell International (1976), a process is described for converting beta-type TiCl.sub.3 to the more active violet TiCL.sub.3 by heating the beta-TiCl.sub.3 in the presence of an organic halide, specifically, certain chlorinated hydrocarbons as specified. As disclosed, the brown TiCl.sub.3 reduced solid is preferably pretreated with a complexing agent, an ether, and washed prior to the organic halide-heat treatment. The addition of the organic halide is described as causing the conversion of the catalyst at a lower temperature, resulting in higher catalyst activity.
Such methods using organic halides, however, have the disadvantage that, in order to obtain a titanium trichloride catalyst component having alpha-olefin polymerization properties, i.e., high stereospecificity and catalytic efficiency, superior to commercially available TiCl.sub.3 catalysts obtained by aluminum reduction and grinding, referred to above, there is necessarily a significant sacrifice in catalyst yield. As known, many organic halides, e.g., chlorinated hydrocarbons, act as solvents for titanium trichloride compositions. Hence, in such known processes there must be some sacrifice in either catalyst yield or overall catalytic performance achieved.